Version:            (using KDE KDE 3.1.2)
Installed from:    Gentoo Packages
Compiler:          gcc 3.2.2 
OS:          Linux

When viewing an attachment, the temporary file created for the application is often deleted too soon.

This is especially a problem when viewing attachments in Open Office since it can take some time to load. Usually in that time I will read the next message in my inbox to pass the time, unfortunately, kmail takes this as a cue that I have finished with the other message and it's attachment and it deletes the attachment that open office was supposed to load.

Perhaps such temporary files could be cleaned up after a certain time out? Or upon exit of kmail?
Or if you wanted to be more accurate, perhaps you could track the process that was launched to view the attachment and wait for that process to exit? Though sometimes that might not be accurate, so maybe combine the two - eg delete the message either when the process exits or when you view a new message, whichever comes later.